Memory is one type of integrated circuitry, and is used in computer systems for storing data. Integrated memory is usually fabricated in one or more arrays of individual memory cells. The memory cells might be volatile, semi-volatile, or nonvolatile. Nonvolatile memory cells can store data for extended periods of time in the absence of power. Nonvolatile memory is conventionally specified to be memory having a retention time of at least about 10 years. Volatile memory dissipates, and is therefore refreshed/rewritten to maintain data storage. Volatile memory may have a retention time of milliseconds, or less.
The memory cells are configured to retain or store memory in at least two different selectable states. In a binary system, the states are considered as either a “0” or a “1”. In other systems, at least some individual memory cells may be configured to store more than two levels or states of information.
Integrated circuit fabrication continues to strive to produce smaller and denser integrated circuits. There is a continuing effort to reduce the number of components in individual devices because such can reduce the size of finished constructions and simplify processing. The smallest and simplest memory cell will likely be comprised of two electrodes having a programmable material, and possibly a select device (such as a diode or ovonic threshold switch), received between them. Suitable programmable materials have two or more selectable memory states to enable storing of information by an individual memory cell. The reading of the cell comprises determination of which of the states the programmable material is in, and the writing of information to the cell comprises placing the programmable material in a predetermined state. Some programmable materials retain a memory state in the absence of refresh, and thus may be incorporated into nonvolatile memory cells.
Phase change materials, such as ovonic memory materials (for instance, various chalcogenides), are being considered for use as programmable materials in memory cells. The phase change materials transform from one phase to another through application of appropriate electrical stimulus, with each phase corresponding to a different memory state.
An example prior art memory array 1 is shown in FIG. 1, and which comprises chalcogenide phase change memory elements. Memory array 1 comprises a plurality of memory cells 2, each including a memory element 3 of the phase change type and a select device 4. Memory cells 2 are interposed at cross-points between row lines 6 (also called wordlines or access lines) and column lines 5 (also called bitlines or sense lines). In each memory cell 2, memory element 3 has a first terminal connected to a wordline 6 and a second terminal connected to a select device 4. The select device 4 has a second terminal connected to a bitline 5.
A problem that may be encountered in the use of chalcogenide materials as memory elements and/or as select devices is that it can be difficult to adhere chalcogenide material to various other materials. Accordingly, delamination of chalcogenide material from adjacent materials may occur. Such delamination can be detrimental to memory cell performance, and in some cases may lead to failure of memory cells. It would be desirable to develop improved memory cells having better adherence of chalcogenide materials to adjacent materials.